netdev - Re: [PATCH bpf-next v4 3/6] bpf: Move is_valid_bpf_tramp

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Date:   Wed, 18 May 2022 11:35:43 +0800
From:   Xu Kuohai <xukuohai@...wei.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
CC:     <bpf@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Zi Shen Lim <zlim.lnx@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
        <hpa@...or.com>, Shuah Khan <shuah@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Daniel Kiss <daniel.kiss@....com>,
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        Sudeep Holla <sudeep.holla@....com>,
        Marc Zyngier <maz@...nel.org>,
        Peter Collingbourne <pcc@...gle.com>,
        Mark Brown <broonie@...nel.org>,
        Delyan Kratunov <delyank@...com>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>
Subject: Re: [PATCH bpf-next v4 3/6] bpf: Move is_valid_bpf_tramp_flags() to
 the public trampoline code

On 5/17/2022 11:53 PM, Alexei Starovoitov wrote:
> On Tue, May 17, 2022 at 03:18:35AM -0400, Xu Kuohai wrote:
>>  
>> +static bool is_valid_bpf_tramp_flags(unsigned int flags)
>> +{
>> +	if ((flags & BPF_TRAMP_F_RESTORE_REGS) &&
>> +	    (flags & BPF_TRAMP_F_SKIP_FRAME))
>> +		return false;
>> +
>> +	/* BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops,
>> +	 * and it must be used alone.
>> +	 */
>> +	if ((flags & BPF_TRAMP_F_RET_FENTRY_RET) &&
>> +	    (flags & ~BPF_TRAMP_F_RET_FENTRY_RET))
>> +		return false;
>> +
>> +	return true;
>> +}
>> +
>> +int bpf_prepare_trampoline(struct bpf_tramp_image *tr, void *image,
>> +			   void *image_end, const struct btf_func_model *m,
>> +			   u32 flags, struct bpf_tramp_links *tlinks,
>> +			   void *orig_call)
>> +{
>> +	if (!is_valid_bpf_tramp_flags(flags))
>> +		return -EINVAL;
>> +
>> +	return arch_prepare_bpf_trampoline(tr, image, image_end, m, flags,
>> +					   tlinks, orig_call);
>> +}
> 
> It's an overkill to introduce a new helper function just to validate
> flags that almost compile time constants.
> The flags are not user supplied.
> Please move /* BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops ... */
> comment to bpf_struct_ops.c right before it calls arch_prepare_bpf_trampoline()
> And add a comment to trampoline.c saying that BPF_TRAMP_F_RESTORE_REGS
> and BPF_TRAMP_F_SKIP_FRAME should not be set together.
> We could add a warn_on there or in arch code, but feels like overkill.
> .

OK, will fix in next version.